This document describes a method and apparatus for enhancing the charge collection function, using third generation telecommunication systems as an example.
The introduction of the third Generation Partnership Project (3GPP) and the third Generation Partnership Project 2 (3GPP2) harmonization effort known as IP (Internet Protocol) Multimedia Sub-system (IMS) has introduced new convergence network elements based on IP based signaling protocols and bearer connections. The goal is to create a harmonized wireless and wireline IP based control network for telecommunications. The IMS network elements include the Proxy-Call Session Control Function (P-CSCF), Interrogating-CSCF (I-CSCF), Serving-CSCF (S-CSCF), Media Gateway Control Function (MGCF), the Breakout Gateway Control Function (BGCF), the Media Resource Function Controller (MRFC), and Application Servers (AS). In order to perform charging functions in the converged IMS network, each of the network elements have a defined interface to a new element called the Charging Collection Function (CCF). CCF, defined in 3GPP (Release 5) and 3GPP2 standards documents, is an off-line charging network element in the IMS network. CCF collects session charging information from IMS elements, and constructs and formats Charging Data Records (CDRs). It provides intermediate data storage buffering and provides a mechanism to transfer charging information to the operator's billing system (BS).
For IMS, the CCF provides the mechanism to transfer charging information from the IMS elements to the operator's chosen Billing System(s). The CCF is responsible for the collection of session charging information from the IMS elements. The CCF may also act as an intermediate data storage device and therefore needs to support storage of CDRs for a specified period of time given a usage profile. Further, the CCF in 3GPP standards must create ASN.1 (Abstract Syntax Notation.1) base Charging Detail Records. These CDRs are transferred to the BS/BMD (Billing Mediation Device) nominally using FIP (File Transfer Protocol), but other protocols and transport methods are possible. The CCF can receive data from the IMS elements in a near real-time mode. It should have enough storage to enable it to transmit the collected charging data to the BS in file mode. The CCF may support several transmission protocols towards the BS. One of the purposes for the CCF is to reduce the number of different interfaces between the BS and the IMS elements sending charging data.
In the IMS system, on-line charging is conducted by an Online Charging Server (OCS). IMS elements query the OCS in real-time with charging information. The OCS rates calls with a built-in rating engine and provides credit control for the session. The OCS also generates CDRs when a call is terminated. The OCS can support both prepaid and postpaid modes.
3GPP and 3GPP2 are generalizing the aforementioned IMS charging architecture to the entire 3G network, which includes Circuit Switch and Packet Switch networks.
However, there are no standards (neither in 3GPP nor 3GPP2) which support the charging and rating concept in CCF so that it cannot provide call cost in CDRs. All rating and billing information must be processed in a back office billing system. That limits the capability of IMS/CCF to postpaid and offline billing only.
U.S. Pat. No. 7,010,104, issued on Mar. 7, 2006, relates to a preliminary concept of the pre-biller which resides in the CCF. The CCF can collect charging information from a Charging Data Record (CDR) and construct a Diameter R0 Credit Control Request (CCR) message to any rating engine to rate the call. The pre-biller will insert received call cost as a new parameter in CDR which can be pulled by the Billing System. However, the patent did not provide information as to when and how the pre-biller function can be operated and executed, and which CDR can be rated via the pre-biller.
The IMS offline charging architecture is changed in 3GPP Release 6 and Release 7 standards. The CCF function is upgraded to a Charging Data Function (CDF) and a Charging Gateway Function (CGF). The CDF interfaces with network elements to receive charging information via Diameter Rf message and create Charging Data Record (CDR) per session (call) per network element, which results in multiple CDRs per session; many network elements may be involved in the session and all send charging information to the CDF. The CGF is a gateway between the CDF and BS/BMD to re-process and store the CDRs.
A problem of the prior art is that since a CCF based pre-biller cannot correlate multiple CDRs in one session because network elements may send charging information to multiple CCFs in the IMS network. A CCF based pre-biller may not have sufficient charging information from one CDR to construct a correct CCR message to the OCS to rate the call.